Oscillation system



March 22, 1932. CQRAM 1,850,580

OSCILLATION SYSTEM Original Filed Dec. 28. 1928 Fla: 2

H. E. Cam/w ATTORNEY Patented Mar. 22, 1932 UNITE STATES PATENT orrics ROY E. G'ORAM, 0F ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, v i

' INCORPORATED, OF NEW YORK, N. Y., A CGRI'ORATION OF NEW YORK' OSCILLATION SYSTEM This invention relates to oscillation systems and particularly to those systems possessing means for producing waves, the frequency of which is constant in respect to especially for radio transmission purposes, to maintain the frequency of oscillations gen- 10 erated substantially constant.

One of the principal causes for such frequency variations arises from the fact that the electrical values of the elements in the frequency-determining circuit vary with temperature.

It is an object of this invention to produce oscillations of a constant frequency in respect to temperature variations affecting the system.

It is another object of this invention to produce constant frequency oscillations in respect to temperature variations without the use of vibrating or moving frequencydetermining elements.

It is still another object of this invention to provide a simple and inexpensive means of obtaining the desired constant frequency oscillations.

According to the present invention these objects, as well as other related and incidental objects, are accomplished by combining waves from component frequency oscillators whose frequency variations caused by temperature changes are equal in degree. A constant sum or difference frequency is obtained, depending on whether the oscillator temperature coefficients have opposite or like signs. V

More specifically, these objects are accomplished; first, by employing an inductance having a negligible coefficient in one of two oscillators so that the temperature-frequency changes result principally from the changes in capacity caused by temperature variation's; then, by choosing for this oscillator a. frequency-determining capacity whose temperature coefficient bears thev proper mathematical relation to that temperature coefiicient which the oscillator must have in order that the frequency variations of the oscillators will be equal to each other in deif Application filed December 28, 1928, Seria1 No. 329,001. Renewed August 7, 1931.

gree; and, finally, by combining the Waves from the oscillators and properly selecting either the sum or difference frequency. The frequency-determining capacity so chosen may be provided by one or several condensers and may, in general, have any value provided that, for a given frequency, the product of the inductance and capacity,and the condenser temperature coefficient have the desired values.

The nature'of this invention will be more fully understood-by reference to the drawings, in which:

Fig. l is a circuit diagram of two electric space discharge oscillatorsand a space discharge modulator embodying in combination oneform of the invention; and

Fig. 2 is a representation of a feed-back arrangement that may be substituted for the circuits comprised between the lines X-X and YY of Fig. 1. p I

Space discharge tubes 1 and 2 with their individual input and output circuits constitute functionally independent oscillators O and 0 Energy is fed back from the output circuit to the input circuit of tube 1 by means of the inductive coupling between windings 6 and 7 of transformer 13. The primary 7 of transformer 13 and condenser 8 comprise oscillation circuit 27 which serves to determine the frequency of the oscillations generated by this oscillator. Similarly, energy is returned from the output to the input circuit of space discharge tube 2 by means of the inductive coupling between the windings 9 and 10 of transformer lt, and the electrically oscillating circuit 27 comprising inductance 10 and condenser 11 determines the frequency of theoscillations generated by. this device.

A source of E. M. F. 3 supplies cathode heating current to space discharge devices 1 and 2. Space current is supplied to tubes 1 and 2 from a common direct current source of energy 4:, which has its positive terminal connected to the anodes of tubes 1 and 2 through the retardation coils 28 and 28, respectively, and its negative terminal connectedto the cathodes of both tubes. The control electrodes of both tubes 1 and 2 are '1 serve in part to complete the alternating ourrent circuits from the frequency determining circuits27iand 27 to the. respective filaments and at thesame time to segregate the source 4 to the individual circuits in which they are intended to function, I

A portion of the output current of each of tubes 1 and 2 is translated by means of the rimar windin s'15 and res acctivell P y I: 1 1 .la

and secondary winding 17 of transformer 18, to the input circuit of a third tube 22. which with its immediately associated circuits constitutes. a modulator or combining device M.

A low impedance path for these output currents to ground and the filaments ofthe respective tubes is provided by condenser 16 which also constitutes a highimped'ance ath for direct current flow from source a. I eating. current forthe cathode of tube 22 is supplied from a source of E..M. F. 20. The space current path includes a direct current source 21 having, its negative terminal connected to the cathode and its positive terminail to the anodethrough a frequency-selecting circuit comprising condenser 23 and the primarywinding 24:, of transformer 25. The secondary winding 26 of transformer 25 may be connected to an amplifier or a work circuit. :A source of steady E. M. F. 19 serves to supply a'negative bias. through secondary windingl'Z to the control electrode of this tube. i i i The operation of the system shown in Fig. 1 as described so far is similarto that of several wellknown oscillator-modulator circuits. Variations in the space current of tube 1 produce. in the oscillation circuit 27 oscillations whose: frequency is determined by the values of capacity 8 and inductance 7. These oscillationsare impressed on the input circuit of tube 1 and amplified in the space curparticular frequency are supplied to the pri- I 7 mary coil 15- .of transformer 18. Similarly,

v, oscillations of the same or another frequency are generated by space discharge tube2 and its associated circuits and supplied to the other primary coil 15 of transformer 18.

Oscillations of both frequencies are induced rent circuit, with the result that waves of a 2 .tain the vibrations of the tuning fork at its natural frequency. Potentials of this frequency are induced in pick-up electromagnet 30 and impressed on the input circuit of tube 1 to perpetuate the current in tromagnet 29. 7 p

In accordance with this inventioncoil 10 is of such a type thatits temperature coeflicientlis small enough to be disregarded, as forexample, an air core coil. The capacity represented by condenser 11 is obtained b the electhe use of one or severalcondensers, pre

erably of a type such as. the so-called dry stack mica condensersdescribed in my pending application, Serial No.. 134,777,. filed September 11,1926. This type of condenser has a comparatively small temperature coefficient. The exact temperature coeflicient of the condensers used to obtain the capacity 11 is determined, however, in accordance with the method to be discussed shortly. Y

Them'ethod of applying the invention will be readily understood from the following.

The percentage temperature coeflicient of space-discharge tube 1 and its associated electrically or mechanically oscillating circuit at a given frequency can readily be calculated or determined from actual tests. Preferably, this oscillator, which has been referred .to as oscillator 0 should be designed to have a known minimum temperature coefiicient as in accordance with the invention disclosed in my prior application,

Serial No. 134,777,1 iled September 11,1926. The temperature-frequency changes inrthe waves produced by this oscillator maybe shown mathematically as follows:

Let a =the known temperature coefficient 1 V of O i j and f =the normal frequency generated and t=temperature difference betweenthe normal and the actual operating temperatures affecting both- O and the other oscillator 0 Then f +1 f t=the actual frequency supr v plied by 0 at any instant 7 and u f t the absolute change in frequency.

In order to obtain constant sum or difierence components in the output of modulator tube 22the above frequency change 'a f t must equal in magnitude the temperaturefrequency change produced in the other oscil- Let f =the normal frequency generated 2 and a =the temperaturecoefiicient of 0 of unknown value constant, when o and or; have like signs (f 7 1 (f f2 =5f1+f2=a constant, when a and a have opposite signs.

And in either case where L and C are the inductance and capacity of the frequency-determining circuit.

Since the frequency varies inversely as the capacity the frequency at any instant resulting from a given change in temperature t from normal may be written:

1 c f2 azfzt 27i' L(0 001 i) (3) Dividing Equation (3) by Equation (2) and squaring we have:

The term (11 2f)? is so small that it may be disregarded and we therefore have:

0' 1 211 i m (5) but 0- 0a t 0 0a t 0-- 00: 7! And, since Coa t is exceedingly small compared to C it maybe disregarded and we have:

from (5) and (7) 1+2a t=1+a t Condensers having a temperature coeflicient equal. to twice the value of the temperature coefficient of the associated oscillator 0 are therefore employed in the frequency-determining circuit of 0 In this connection it should be observed that the value of capacity 11 or the number of individual condensers comprising capacity 11 are not controlled by the temperature coeflicient 11 These factors are determined from other practical considerations.

Substituting the value of a shown in (8) in (1) we have:

await-l;

This last equation gives us a quick and simple method of determining the condenser temperature coefficient of one oscillator in terms of the known temperature coefficient of another oscillator and the frequencies normally generated by the two oscillators.

Because of the approximate mathematics the frequency components are substantially, and not absolutely, constant. In carrying out the invention the best results will be obtained by keeping the frequency changes as small as practicable. This is accomplished by designing the high frequency oscillator corresponding to oscillator 0 so as to have a minimum temperature coefficient.

It should, of course, be understood that the invention is not to be limited to the frequency producing means illustrated in the specific embodiment described above. The invention is equally applicable to other specific wave producing systems wherein the, frequencies supplied to a combining means are affected by temperature changes as, for example, in a double modulation wave producing system.

Also, in order to reduce any error that might arise from the fact that the frequencyf determining elements are not subjected to exactly the same temperature change the elements of both oscillators are preferably located relatively close together in the same room or oven.

What is claimed is 1. In an oscillation system, a plurality of wave generating means, means for combining the waves from said generating means to produce a resultant wave, one of the said generating means including an electrical oscillating element adapted to equalize the temperature-frequency changes in the waves produced by said last mentioned means and another of the said generating means wheref by the resultant-waveis substantially free from temperature-frequency effects.

2. In an oscillationsystem, a plurality of wave genera-ting means, 'meansl' ointly dependent on said first'mentioned means for producing other waves, one of said generating means comprising a frequency-control ling non-vibratory element adapted to comensate for temperature-frequency changes in the waves produced by another of said gen erating means, whereby at least one of the a resultant 'wavesis substantially free from temperature-frequency changes.

3. In combination, an oscillating system comprising an oscillator havlng afrequency F and a temperature coeflicient of frequency T and a second oscillator having a frequencyF controlled by an element having a temperature coefficient of frequencyfl where element included in one of the said means having a temperature coefficient of frequency equal to twice that of the associated means, 7 the frequency changes caused by temperature variations'in the said associated means by choiceof the corresponding coeflicient of said frequency-determining element being equivalent to those produced in another of the said means, and means for combining the produced waves.

6. A constant frequency wave-producing system'comprising a wave producing means, a second wave producing means, a non-vibratory element adapted to control said-second means-to intermodulate said waves;

which equals that ofthe other oscillator, and

, 8.; The method of l obtaining sustained V waves of a constant frequencyllutilizing a modulator and componentoscillators one of which has a known temperature coeflicient and another of which has anon-vibratory frequency' determining element which comprises designing said element so that the ratio of its temperature coefiicient of frequency to the said known temperature coeflicient equals twice the reciprocal of the frequencies generatedby the oscillators, producing waves in said oscillators, and modulating the produced waves. I r

9. The method of producing waves of a constant frequency in respectto temperature variations utilizing a modulator and component oscillators the frequency of atleast one of i which is partly controlled by an element a which comprises choosing an element having a temperature coefficient of frequency such that the'frequency-vari ations in therwave produced by the associated oscillator equals the tem era-ture frequency variations of another of tie oscillators, generating waves in said oscillators, combining the waves in said modulator, and selecting a constant frequency component in the modulator output} 7 10, Means for producing oscillations of a constant frequency comprisinga plurality of cooperatingoscillators from each of which oscillations of varying frequency are derived, means for substantially equalizing the frequency+temperature variations in the oscillations derived from said oscillators, and means for combining said oscillations.

11. In combination, means. for producing distinct sets of oscillations each having frequency-temperature variations, and means for substantially equalizing the frequencytemperature variations in said sets of oscillations. Y ,7

, In witness whereof, I hereunto subscribe my name this 18th dayrof December, 1928.

' f ROY E; CORAlWL means and having a temperature coefficient 7 suitable for rendering the frequency changes caused byfltemperatur'e variations in. the waves producedfequal to each other, and means for combining thewaves. V

7. A system for obtaining Waves of a constant frequency comprising an oscillator, a

' second oscillator including a frequencydetermining capacity, whose-variation with temperature substantially determines the temperature frequency changes in-the waves generated, the value of said capacity being suchthat its variations with temperature cause a corresponding frequency change 

